Certain multi-speed transmissions are characterized by differences in the amount of torque a clutch is subjected to in various gear states. The torque capacity of a clutch is, at least in part, determined by the axial force exerted on the clutch plates and discs by a hydraulically actuated piston. The force of the piston is determined by the pressure of the hydraulic fluid and the surface area of the piston exposed to the hydraulic fluid. Thus, the surface area of a clutch piston exposed to hydraulic pressure must be sized to produce the amount of axial force necessary for the highest torque condition of the clutch.
A clutch with a large torque capacity has a large gain between hydraulic pressure exerted on the piston and clutch torque. Small errors in pressure control may result in large clutch torque errors. In speed ratios with lower mechanical gains, the resulting clutch torque errors can be a significant percentage of the total torque required to complete a shift.